JP2002240725A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the number of assembling and inspecting man-hours for an electric power steering device. SOLUTION: This electric power steering device 10 is comprised of a rack 32 in one side of one end part of a rack shaft 26 extended in the car width direction, a steering pinion 31 is geared with the rack 32, a screw part 71 is formed in a part of the rack shaft 26 except for the rack 32, a nut 73 of a ball screw 70 is assembled with the screw part 71 via a ball, and a hollow motor shaft surrounding the rack shaft 26 is connected to the nut 73. This constitution allows auxiliary torque generated by a motor 50 to be applied to the rack shaft 26 from the motor shaft via the nut 73 according to the steering torque. The nut 73 is disposed between the rack 32 and the motor 50.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement of an electric power steering device.

[0002]

2. Description of the Related Art In recent years, electric power steering devices have been frequently used to reduce the steering force of a steering wheel to provide a comfortable steering feeling. In this type of electric power steering apparatus, an electric motor generates an auxiliary torque corresponding to a steering torque, and transmits the auxiliary torque to a rack shaft of a steering system. An outline of a general electric power steering device will be described below.

FIGS. 11 (a) and 11 (b) are schematic views of a conventional electric power steering apparatus, in which (a) shows the entire configuration and (b) shows the detailed structure of the main part of (a). In a conventional electric power steering apparatus 200, a rack 202 is formed at one end of a rack shaft 201 extending in the vehicle width direction, and a pinion 2 of a pinion shaft 203 is formed on the rack 202.
04 and a screw portion 205 is formed at the other end of the rack shaft 201, and the screw portion 205 is
06 are assembled via balls 208..., And the motor shaft 213 of the motor 211 is connected to the nut 207.

[0004] The pinion shaft 203 is a steering shaft connected to a steering wheel (not shown). The screw portion 205
It is a male screw formed over a predetermined length from the other end of the rack shaft 201. The housing 221 for slidably housing the rack shaft 201 is an elongated storage member including a first housing 222 on the rack side and a second housing 223 on the electric motor side. The electric motor 211 is disposed between the rack 202 and the nut 207 on the rack shaft 201. The auxiliary torque generated by the electric motor 211 is transmitted from the electric motor shaft 213 to the rack shaft 2 via the nut 207 in accordance with the steering torque applied to the steering wheel.
01 can be added.

[0005] As shown in FIG.
Is one end 21 of the motor shaft 213 in the rotor 212.
3a is supported non-slidably and rotatably via a bearing 224. The second housing 223 rotatably supports the other end 213b of the motor shaft 213 via a bearing 225. The motor shaft 213 is a hollow shaft surrounding the rack shaft 201, and has a nut 207 integrated with the other end. 231 is a stator, 232 is a lock nut for a bearing, 233 is a lock nut for a motor shaft, 234 is a stopper for positioning the motor shaft,
235 is a lock nut for fixing the nut, 236 is a cylindrical commutator on the motor shaft side, 237 is a brush on the fixed side, and 238 is a bolt for connecting the first and second housings.

[0006]

As shown in FIG. 11B, the conventional electric power steering apparatus 200 is
An electric motor 211 is arranged between the rack 202 on the first housing 222 side and the nut 207 on the second housing 223 side, and the first housing 222 supports one end 213a of the electric motor shaft 213 in a non-slidable manner. 22
3, the other end 213b of the motor shaft 213 is supported, and the other end 213b supports the nut 207.

A general assembly and inspection procedure of the electric power steering apparatus 200 is as follows (1) to (8). (1) In the second housing 223 which also serves as a motor case,
The components of the electric motor 211 are assembled. (2) The quality inspection and performance test of the electric motor 211 are performed, and then the electric motor 211 is once disassembled. (3) A nut 207 is attached to the other end 213b of the motor shaft 213.
Assemble. (4) Connect one end 213a of the motor shaft 213 to the bearing 224.
And the first housing 22 via the members 232 to 234
Assemble to 2. (5) Each component of motor 211 and second housing 2
23 is attached to the first housing 222. (6) Attach the rack shaft 201. Thus, the assembly of the electric power steering device 200 is completed. (7) The quality inspection and performance test of only the electric motor 211 are performed again. (8) Quality inspection and performance test of the electric power steering device 200 are performed.

[0008] Thus, the electric power steering device 2
00, after assembling the motor 211 and performing a quality inspection and a performance test, the motor 211 is once disassembled and the rack shaft 2 is disassembled.
01 and the ball screw 206. Therefore, the number of steps for assembling and inspecting the electric power steering device 200 increases, which causes a cost increase, and there is room for improvement.

It is an object of the present invention to provide a technique capable of reducing the number of assembling and inspection steps of an electric power steering apparatus.

[0010]

In order to achieve the above object, a first aspect of the present invention is to form a rack on one side of one end of a rack shaft extending in the vehicle width direction, and engage a steering pinion with the rack. A screw portion is formed on the portion of the rack shaft other than the rack, a nut of a ball screw is attached to the screw portion via a ball, and a hollow motor shaft (output shaft of the motor) surrounding the rack shaft is connected to the nut. By doing so, in an electric power steering apparatus in which an auxiliary torque generated by an electric motor according to a steering torque is added from a motor shaft to a rack shaft via a nut, the nut is arranged between the rack and the electric motor. Features.

A nut for a ball screw can be previously assembled to the electric power steering device, and the motor shaft can be connected to this nut later. Therefore, after assembling the motor and performing a quality inspection and a performance test, the motor can be assembled into the rack shaft and the ball screw without being disassembled without being disassembled. Furthermore, there is no need to re-perform the quality inspection and performance test of the motor alone after the motor is assembled into the rack shaft and the ball screw. Therefore, the number of assembly steps and the number of inspection / test steps can be reduced, so that the cost of the electric power steering device can be reduced. In addition, since there is no work of disassembling and reassembling the motor once, it is easy to maintain the assembly accuracy of the motor.

A second aspect of the present invention is characterized in that the motor shaft and the nut are connected to each other in a longitudinal direction of the rack shaft so as to transmit torque. The motor shaft and the nut can be connected to each other so as to be able to transmit torque only by fitting each other in the longitudinal direction of the rack shaft. Therefore, the man-hour for assembling the motor shaft and the nut can be further reduced.

According to a third aspect of the present invention, the motor is provided with a commutator mounted on the motor shaft and a brush contacting a brush contact surface of the commutator, and the brush contact surface is a surface orthogonal to the motor shaft. And For the brush contact surface of the commutator,
The brush is applied from the axial direction of the motor shaft. For this reason, when assembling the motor, the assembling direction of the commutator and the brush can be matched with the assembling direction of the motor shaft. Therefore, assemblability can be improved.

According to a fourth aspect of the present invention, a rack guide for extruding the rear surface is disposed on the rear side of the surface of the rack shaft on which the rack is formed, and the rack shaft is located at a position closer to the other end than the threaded portion. A bush for supporting the rack shaft when it is bent by a predetermined value is arranged. When an external force due to a road surface reaction force or a moment is generated at both ends of the rack shaft and the other end of the rack shaft is bent by a predetermined value, the other end can be supported by the bush. Therefore, the other end of the rack shaft does not bend more than the predetermined value. Since the amount of deflection is small, vibration of the rack shaft can be easily suppressed.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The drawings should be viewed in the direction of reference numerals. FIG. 1 is a schematic diagram of an electric power steering device according to the present invention. The electric power steering device 10 includes a steering system 20 extending from the steering wheel 21 of the vehicle to the steered wheels 29, 29, and an auxiliary torque mechanism 40 for applying an auxiliary torque to the steering system 20. The electric power steering device 10 is an end take-off type steering device that takes out a steering torque from both ends of a rack shaft 26.

The steering system 20 comprises a steering wheel 21 and a steering shaft 22 and a universal joint 2.
A pinion shaft 24 is connected to the pinion shaft 24 via a rack and pinion mechanism 25, and left and right tie rods 27, 27 and knuckles 28, 28 are connected to both ends of the rack shaft 26. The left and right steering wheels 29 are connected to each other via the same.

The rack-and-pinion mechanism 25 is formed by engaging a pinion 31 formed on a pinion shaft 24 with a rack 32 formed on one side of a rack shaft 26.
By the driver steering the steering wheel 21,
With this steering torque, the left and right steering wheels 29, 29 can be steered via the rack and pinion mechanism 25 and the left and right tie rods 27, 27.

The auxiliary torque mechanism 40 detects a steering torque of the steering system 20 applied to the steering wheel 21 by a steering torque sensor 41, generates a control signal by a control means 47 based on the detected signal, and generates a control signal based on the control signal. An auxiliary torque corresponding to the steering torque is generated by the electric motor 50,
The auxiliary torque is transmitted to the rack shaft 26 via a ball screw 70 as a torque transmitting member.

In summary, the electric power steering device 10 transmits the steering torque applied to the steering wheel 21 of the vehicle to the rack shaft 26 via the rack and pinion mechanism 25, and also controls the electric motor 50 according to the steering torque. Is applied from the motor shaft of the electric motor 50 to the rack shaft 26 via the ball screw 70,
The steering wheels 29, 29 are steered by the rack shaft 26. Therefore, the steering system 20
The steering wheels 29, 29 can be steered by the combined torque obtained by adding the auxiliary torque of the electric motor 50 to the steering torque of the steering wheel 29.

FIG. 2 is an overall configuration diagram of the electric power steering apparatus according to the present invention, and shows a cross section of a main part. The electric power steering device 10 includes a rack and pinion mechanism 25, an electric motor 50, and a ball screw 70.
Is housed in a housing 101 extending in the vehicle width direction (the left-right direction in the figure).

The housing 101 is assembled into one elongated gear box by connecting one end surfaces of a generally tubular first housing 102 and a second housing 103 with bolts. The first housing 102 includes a bracket 104 for attaching to a vehicle body (not shown). The second housing 103 also functions as a motor case in the motor 50.

The rack shaft 26 extending in the vehicle width direction is a shaft penetrating the housing 101 so as to slide in the vehicle width direction. Such a rack shaft 26 has one end on the right side in the figure connected to the rack-and-pinion mechanism 25, a substantially longitudinal center position connected to the ball screw 70, and the other end on the left side in the figure (the other end than the ball screw 70 (At a position closer to the side). That is, the ball screw 70 is arranged between the rack and pinion mechanism 25 and the electric motor 50.

According to the present invention, the rack 32 is formed at one end of the rack shaft 26, a screw portion 71 is formed at a portion of the rack shaft 26 other than the rack 32, and a ball screw 70 is formed at the screw portion 71. A nut 73 is assembled, a hollow motor shaft 56 surrounding the rack shaft 26 is connected to the nut 73, and the nut 73 is arranged between the rack 32 and the motor 50. In other words, the electric motor 50 is arranged at a position closer to the other end of the rack shaft 26 than the nut 73.

In the housing 101, a rack guide 120 is arranged at a center position where the pinion 31 and the rack 32 mesh with each other, and the rack shaft 26 is located at a position closer to the other end (left end in the figure) than the screw portion 71 of the rack shaft 26. The bush 105 is arranged. The bush 105 is a member that supports the rack shaft 26 when it is bent by a predetermined value. By the way, rack shaft 2
Reference numeral 6 indicates that the diameter of the portion without the screw portion 71 is set smaller than the root diameter of the screw portion 71. The rack guide 120 will be described in detail with reference to FIG.

Here, in the vehicle width direction, the pinion 31
The position of the center of engagement of the ball screw 70 with the rack 32 is A (hereinafter, referred to as “pinion center A”), and the center of the ball screw 70 in the axial direction is B (hereinafter, referred to as “ball screw center B”). The center position of the bush 105 is referred to as C (hereinafter, referred to as “bush center C”). In the figure, 10
6, 106 are ball joints; 107, 107 are dust seal boots.

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2, and shows a longitudinal sectional structure of the electric power steering apparatus 10. As shown in FIG. The electric power steering device 10 includes a rack and pinion mechanism 25 and a steering torque sensor 41 that are connected to the first housing 10.
2 and the upper opening of the first housing 102 is closed by a lid 108.

The pinion shaft 24 has an upper first shaft 24A connected to the steering wheel 21 (see FIG. 1),
Lower second shaft 24B integrally formed with pinion 31
And a torsion bar 24C connecting the first and second shafts 24A and 24B. Torsion bar 24
C is a member in which the torsion angle is generated exactly with respect to the torque, and the first shaft 24A and the second shaft 24B
This is an elastic member that generates a relative torsional displacement between.

The steering torque sensor 41 detects a steering torque according to the relative torsion angles of the first and second shafts 24A and 24B, and includes a slider 42 and a variable inductance sensor 46. It is a torsion bar type torque sensor. More specifically, the steering torque sensor 41 slidably fits a cylindrical slider 42 to the first and second shafts 24A and 24B.
2 and the oblong straight groove 44
With the pin 45A of the first shaft 24A and the second shaft 24B
And a pin 45B.

The slider 42 has first and second shafts 24A,
It can slide up and down according to the relative torsional displacement of 24B. The sliding amount of the slider 42 at this time is proportional to the torque. The sensor unit 46 converts the sliding amount into an electric signal, and can output the electric signal to the control unit 47 (see FIG. 1) as a steering torque detection signal.

In the drawing, reference numeral 48 denotes a spring for springing a slider, 49 denotes a terminal for a steering torque sensor, 111 denotes a first shaft bearing, 1
Reference numerals 12 and 113 denote second shaft bearings, 114 and 115 are retaining rings, 116 is a nut, 117 is a cap nut, 118 is an oil seal, and 119 is an O-ring.

The rack guide 120 serves to push the rear surface of the rack shaft 26 to the rear surface of the surface on which the rack 32 is formed. More specifically, the rack guide 120 includes a guide portion 121 that contacts the rack shaft 26 from a side opposite to the rack 32, and an adjustment bolt 123 that presses the guide portion 121 via a compression spring 122. According to such a rack guide 120, the first housing 1
02 with the adjusting bolt 123 screwed into the compression spring 12
By pressing the guide portion 121 with an appropriate pressing force via the second member 2, a preload is applied to the rack 32 by the guide portion 121, and the rack 32 can be pressed against the pinion 31. 12
4 is a contact member for sliding the back surface of the rack shaft 26, and 125 is a lock nut.

FIG. 4 is a sectional view of a main part around a rack shaft, an electric motor, and a ball screw according to the present invention. The electric motor 50 is
A cylindrical yoke 51 made of a ferromagnetic material fitted in the housing 103, and a plurality of stators 52 made of permanent magnets arranged in the yoke 51 are shown.
Are arranged in a state where these stators 52 are aligned.
External stator holder 53 mounted in housing 103
And the internal stator holder 54 and the stator 52.
(I.e., the inside of the internal stator holder 54).

The rotor 55 includes a tubular motor shaft 56 rotatably fitted to the rack shaft 26 and a motor shaft 56.
A coil 57 wound around the outer peripheral surface of the core 57, and a commutator 59 connected to the coil 58. Thus, the motor shaft 56 is a hollow output shaft surrounding the rack shaft 26.
The inner diameter of the motor shaft 56 is larger than the outer diameter of the screw portion 71.

The commutator 59 is attached to the outer periphery of the motor shaft 56 on the side of the coil 58, and is connected to the rack shaft 26.
The flat surface facing the left end side (the left side in the figure) is the brush contact surface 59.
a. That is, the brush contact surface 59a is
6 is orthogonal to FIG. Brush contact surface 59 of commutator 59
The brush 61 that comes into contact with a is housed in the second housing 103 via the brush holder 62.

With respect to the brush contact surface 59a, the motor shaft 5
6, the brush 61 is applied from the axial direction. Therefore, when assembling the electric motor 50, the assembling direction of the commutator 59 and the brush 61 can be matched with the assembling direction of the electric motor shaft 56. Therefore, the assemblability of the electric motor 50 can be improved. 63 is a compression spring for firing a brush, 6
4 is a brush cord.

The ball screw 70 has a screw portion (male screw) 71 formed on the rack shaft 26 and a large number of balls 72.
And a nut 73 of an outer cylinder portion attached to the screw portion 71 via balls 72. The ball screw 70 transmits the auxiliary torque of the electric motor 50 from the nut 73 to the screw portion 7 via the ball 72.
1 and the ball 72... Reaching the end of the thread groove of the nut 73 circulates through a tube (not shown). It is.

The first housing 102 rotatably supports the output end 56a of the motor shaft 56 via the nut 73 of the ball screw 70 and the first bearing 131. The second housing 103 is connected to the non-output end 56 of the motor shaft 56 via the second bearing 132 and the bush 133.
c is rotatably supported. First and second bearings 1
31 and 132 are rolling bearings. Bush 133
Are the inner peripheral surface of the second housing 103 and the second bearing 132
Are members interposed between the outer ring and the outer peripheral surface of the outer ring.

More specifically, the first housing 102 integrally forms a ball screw housing 102b for fitting into the second housing 103.
The nut 73 is rotatably supported in a second bearing 2b via a first bearing 131. The first bearing 131 is configured such that the axial movement with respect to the first housing 102
4, and rotatably supports the center of the nut 73 or a position in the vicinity thereof.

The nut 73 includes a support portion 74 fitted to the first bearing 131, a large-diameter portion 75 connected to one end of the support portion 74 and having a larger diameter than the support portion 74, and a connection hole 76 formed in the support portion 74. Consists of First bearing 131 fitted to bearing 74
Is sandwiched between the large-diameter portion 75 and the lock screw 135 so that the nut 7 with respect to the first housing 102 is
3 can be restricted from moving in the axial direction. As a result, the nut 73 is rotatable and immovable in the axial direction (not slidable).

The output end 56a of the motor shaft 56 is connected to the nut 7
As described above, the first housing 102 rotatably supports the output end 56a of the motor shaft 56 via the nut 73 and the first bearing 131 by being fitted and connected to the third connection hole 76. Can be. Output end 5 of motor shaft 56
Reference numeral 6a denotes an axial movement to the right side in the figure, which is regulated by its tip hitting the step 77. The configuration in which the output end 56a cannot move in the axial direction will be described in detail with reference to FIG. On the other hand, the non-output end portion 56c of the motor shaft 56 is such that the step 56d at the tip thereof contacts the end surface of the inner ring of the second bearing 132, whereby the axial movement to the left in the figure is restricted. As a result, the motor shaft 56 cannot move in the axial direction.

Further, this figure shows that the flange 103a at one end of the second housing 103 is connected to the flange 102a at one end of the first housing 102 by bolts 136. In the figure, 137 and 138 are spacers, and 139 is an O-ring.

FIG. 5 is a sectional view showing the connection structure between the electric motor and the ball screw according to the present invention. The present invention provides the motor shaft 5
The nut 6 and the nut 73 are connected to each other in a longitudinal direction of the rack shaft 26 so as to transmit torque. Further, the present invention is characterized in that a torque limiter 90 is added between the motor shaft 56 and the ball screw 70 so that a torque equal to or more than a predetermined value is not transmitted. A specific connection structure between the motor shaft 56 and the nut 73 will be described below.

In the motor shaft 56, a groove 56b having a constant width is formed on the outer peripheral surface of the output end portion 56a over the entire circumference.
6b has a torque limiter 90 fitted therein. On the other hand, the nut 73 forms a connection hole 76 concentric with the rack shaft 26 on the input side, and the diameter of the connection hole 76 is
The diameter is set to be larger than the inner diameter of the part provided with. For this reason, a step 77 is provided at the back end portion of the connection hole 76. By fitting the output end 56a of the motor shaft 56 into the connection hole 76 of the nut 73, the output end 56a and the connection hole 7
6, a torque limiter 90 can be interposed. Further, the output end 56a fitted into the connection hole 76
Is moved rightward in the figure (ball 7
2) is restricted.

The electric motor shaft 56 and the nut 73 can be connected to each other so as to be able to transmit a torque only by fitting each other through the torque limiter 90 in the longitudinal direction of the rack shaft 26. Accordingly, the number of steps for assembling the motor shaft 56 and the nut 73 can be further reduced.

FIGS. 6A and 6B are exploded views showing the connection structure of the electric motor, the ball screw and the torque limiter according to the present invention. (A) shows the motor shaft 56, the nut 73, and the torque limiter 90 disassembled. (B) is an enlarged view of part b of (a). The torque limiter 90 is
The width is constant and the thickness is extremely small (for example, 0.3 m
m) Based on an annular metal band 91, only one portion around the band 91 is cut. Band 91
Is formed integrally with a plurality of engaging ridges 92 which are elongated in the axial direction at a constant pitch (for example, a pitch of 6 to 7 mm) in the circumferential direction over the entire outer peripheral surface. These engaging ridges 92... Are formed, for example, by pressing the band 91, so that the height and length of the projecting portions (for example, height 0.7 mm, Length 9
mm), and the tip of the projection has an arc-shaped cross section.

Such a torque limiter 90 is a member that blocks transmission of torque of a certain level or more, and is generally called a tolerance ring. By fitting the inner surface of the band 91 to the bottom surface of the groove 56b in the motor shaft 56 and fitting the circumferential surface of the connection hole 76 to the tip end surface of each of the plurality of engaging ridges 92.
Torque can be transmitted by the frictional force between these members. Further, the plurality of engaging ridges 92... Can elastically deform radially inward of the band 91 in accordance with a torque equal to or greater than a predetermined value. As the engaging ridges 92 are deformed, the frictional force between the members 56, 73, and 90 is reduced.

Returning now to FIG. 5, the motor shaft 56,
The operation of the nut 73 and the torque limiter 90 will be described.
The auxiliary torque generated by the electric motor 50 is transmitted to the rack shaft 26 through a path of the electric motor shaft 56, a torque limiter 90, a nut 73, a ball 72,. As a result, the auxiliary torque can be converted into thrust (axial force on the rack shaft 26) and applied to the rack shaft 26.

On the other hand, when a torque equal to or more than a predetermined value acts on the torque limiter 90, the engaging ridges 92...
The frictional force between 6, 73, 90 decreases. As a result, no more than a certain torque is transmitted between the motor shaft 56 and the nut 73. Therefore, no excessive torque acts on the electric motor 50.

FIG. 7 is an explanatory view of an assembling procedure of the electric motor according to the present invention. The assembling procedure of the motor 50 is as follows (1) to (7).
It is as follows. (1) Prepare the second housing 103 in which the yoke 51 is incorporated. (2) The second bearing 132 and the bush 133 are incorporated into the second housing 103 from one end side (that is, the opening 103b on the flange 103a side). (3) Brush holder 6 incorporating brushes 61
2 is assembled into the second housing 103 from one end side. (4) A plurality of stators 52 are assembled into external and internal stator holders 53 and 54 to form a stator block. (5) The stator block is assembled into the second housing 103 from one end. (6) The rotor 55 including the motor shaft 56, the coil 58, and the commutator 59 is assembled into the second housing 103 from one end. (7) As a result, the rotor 55 is
And the motor shaft 56 can be incorporated in the second bearing 132. At the same time, the brush contact surface 59a can be brought into contact with the brushes 61,61.

Thus, the assembling work of the electric motor 50 is completed.
In this manner, all the motor components can be assembled in the second housing 103 from the opening 103b on the flange 103a side, that is, from one side in the axial direction of the motor shaft 56. Since all parts can be assembled from one direction, assembly of the electric motor 50 is easy, assemblability can be improved, and automatic assembly can be performed.

FIG. 8 is a view showing a completed motor and an assembling procedure of the electric power steering apparatus according to the present invention. This figure shows the completed motor 50. A quality inspection and a performance test of the electric motor 50 assembled as shown in this figure can be performed. When performing the performance test, the output end 56a of the motor shaft 56 is rotatably supported by a jig. Thereafter, the torque limiter 90 is attached to the output end 56a.

The procedure for assembling the electric power steering device 10 is as follows (1) to (4). (1) The nut 73 of the ball screw 70 is assembled in the first housing 102. (2) The rack shaft 26 is passed through the first housing 102 to be incorporated into the ball screw 70 (arrow). (3) Connect the output end 56a to the connection hole 76 with the rack shaft 2
6 (arrows) in the longitudinal direction of the motor shaft 5
6 is connected to a nut 73 via a torque limiter 90. At the same time, the opening 103b is
Fits. (4) Connect the flange 103a to the flange 102a with the bolt 1
Connect at 36. With the above, the electric power steering device 1
0 is completed.

After the motor 50 has been assembled and quality inspection and performance tests have been performed, the rack shaft 26 and the ball screw 7 are assembled without disassembling the motor 50.
0.

Further, after the electric motor 50 is assembled into the rack shaft 26 and the ball screw 70, it is not necessary to re-perform the quality inspection and the performance test of the electric motor 50 alone. Therefore, the number of assembly steps and the number of inspection / test steps can be reduced, so that the cost of the electric power steering apparatus 10 can be reduced. In addition, since there is no work of disassembling and reassembling the electric motor 50, it is easy to maintain the assembly accuracy of the electric motor 50.

To summarize the above description, the present invention is as follows. The present invention, as shown in FIG.
To the other end of the rack shaft 26 relative to the nut 73 (left side in the figure)
The motor shaft 56 and the nut 73 are separated from each other, and the motor shaft 56 and the nut 73 are connected to each other in the longitudinal direction of the rack shaft 26 so that torque can be transmitted. It is characterized by having done.

In other words, the electric power steering apparatus 10 of the present invention has the following features. (1) The nut 73 is arranged between the rack 32 (see FIG. 2) on the first housing 102 side and the electric motor 50 on the second housing 103 side. (2) The electric motor 50 is housed in the second housing 103, (3) the nut 73 is supported by the first housing 102 so as to be rotatable and restricted from moving in the axial direction. Axis 56
(5) that the output end 56a of the motor shaft 56 is rotatably supported by being fitted in the longitudinal direction of the rack shaft 26 so that the second housing 103 rotatably supports the other end 56c of the motor shaft 56. Features.

Therefore, the electric power steering device 10
First (ie, in the first housing 102),
The motor shaft 5 is attached to the nut 73 later.
6 can be connected. For this reason, after assembling the motor 50 and performing a quality inspection and a performance test, the motor 50
Can be easily assembled into the rack shaft 26 and the ball screw 70 in an assembled state without disassembly.

FIGS. 9A to 9D are diagrams for explaining the operation of the electric power steering apparatus according to the present invention. FIG. 9 (a)
FIG. 3 is a schematic plan view in which the electric power steering apparatus 10 of FIG. 2 is combined with the system of FIG. 1. In addition,
The reference numerals of the respective parts are the same as those shown in FIGS. 1 and 2, and the description thereof will be omitted. The bush 105 has a gap δ having a predetermined size to support the rack shaft 26 when the rack shaft 26 is bent by a predetermined value.

FIG. 9B is a further schematic diagram around the rack shaft 26 shown in FIG. 9A. The rack shaft 26 is supported by a pinion center A and a ball screw center B. This indicates that the rack guide 120 has pressed the rack. More specifically, since the ball screw 70 is assembled to the rack shaft 26, the ball screw 70 supports the rack shaft 26 from the front and rear of the vehicle body. The pinion 31 supports the rack shaft 26 from the front of the vehicle body, and the rack guide 12
Numeral 0 indicates that the rack shaft 26 is pressed from the rear of the vehicle body. Moreover, the bush 105 supports the rack shaft 26 when the rack shaft 26 is bent at a predetermined value at the bush center C.

FIG. 9C is a schematic operation diagram (first) around the rack shaft 26 shown in FIG. 9B, and FIG.
Schematic action diagram around the rack shaft 26 shown in (b) (second)
It is. At the both ends of the rack shaft 26, a road surface reaction force during traveling, particularly during steering, and an external force caused by the ball screw 70 act or generate a moment (hereinafter, "moment Mf from the front of the vehicle body", " Moment Mr ").

As shown in FIG. 9C, the end of the rack shaft 26 is bent away from the pinion 31 by the moments Mf and Mf from the front of the vehicle body. Rack shaft 26
When the left end of the figure is bent by a predetermined value, the rack shaft 26 is supported at three points of the ball screw 70, the bush 105, and the rack guide 120. As a result, the rack shaft 26 bends as shown by the thick solid line in FIG. The bent solid line is a swing waveform when the rack shaft 26 is deformed rearward.

On the other hand, as shown in FIG. 9D, the end of the rack shaft 26 is bent in a direction of pressing against the pinion 31 by the moments Mr and Mr from the rear of the vehicle body. When the left end of the rack shaft 26 is bent by a predetermined value, the rack shaft 26 is moved to the pinion 31, the ball screw 70, and the bush 105.
You will be supported by points. As a result, the rack shaft 26 bends as shown by the thick solid line in FIG. The bent solid line is a swing waveform when the rack shaft 26 is deformed forward.

As is clear from the above description, the moments Mf and Mr from the front and rear of the vehicle body act on both ends of the rack shaft 26, and when the left end of the rack shaft 26 is bent by a predetermined value, the rack shaft 26 is supported by the bush 105. As a result, the left end does not bend more than the predetermined value. Since the deflection amount is small, the vibration of the rack shaft 26 can be easily suppressed.

As described above, when the vibration of the rack shaft 26 is suppressed, the vibration of the steering handle is also suppressed, so that the steering feeling is enhanced. Also, vibration transmitted to the vehicle interior via the steering wheel is suppressed,
Noise in the cabin can be prevented.

FIGS. 10 (a) to 10 (d) are explanatory views of the manufacturing procedure of the rack shaft according to the present invention. To manufacture the rack shaft 26, the following steps (a) to (d) are performed. First, in (a), a round bar 26A made of a steel material is continuously supplied to a rolling machine 151. The rolling machine 151 is a differential speed rolling machine provided with two round dies 152 and 153 having different peripheral speeds V1 and V2. Round bar 2 at half the speed of peripheral speed V1, V2
While the 6A is being moved, the thread portion 71 can be continuously threaded into the round bar 26A by through rolling. Next, the round bar 26A on which the screw portion 71 is formed is cut by the cutter 154 at a predetermined length to obtain a semi-finished shaft 26B shown in FIG.

Thereafter, as shown in (c), the semi-finished shaft product 26B
Are opened at both ends of the ball screw. Further, in (c), a small-diameter portion 36 having a smooth surface is formed by cutting the outer peripheral surface of the semi-finished shaft product 26B except for a portion requiring the screw portion 71. The diameter of the small diameter portion 36 is smaller than the root diameter of the screw portion 71.

Finally, the rack 32 is formed on a part of the small diameter portion 36 to obtain the rack shaft 26 as shown in FIG. Thus, the rack shaft 26 can be manufactured.

The above manufacturing procedure has been described in order to clarify the configuration of the rack shaft 26 having the above configuration, and the manufacturing method and the manufacturing procedure are arbitrary. For example, the threaded portion 71 may be obtained by threading only a necessary portion of the rack shaft 26. Such thread processing methods include cutting and in-field rolling.

In the above embodiment of the present invention,
The steering torque sensor 41 is not limited to the torsion bar type torque sensor, and may be, for example, a magnetostrictive torque sensor. When the magnetostrictive torque sensor is adopted, the pinion shaft 24 is connected to the upper and lower shafts 24A,
24B can be an integral shaft. Also, the motor shaft 5
The connection structure between the nut 6 and the nut 73 may be any structure that is connected to each other in the longitudinal direction of the rack shaft 26 so that torque can be transmitted. For example, the connection structure is connected via a spline or serration. Is also good.

[0070]

According to the present invention, the following effects are exhibited by the above configuration. Since the nut is arranged between the rack and the electric motor, a nut for a ball screw can be assembled first in the electric power steering device, and the electric motor shaft can be connected to the nut later. Therefore, after assembling the motor and performing a quality inspection and a performance test, the motor can be assembled into the rack shaft and the ball screw without being disassembled without being disassembled. Furthermore, there is no need to re-perform the quality inspection and performance test of the motor alone after the motor is assembled into the rack shaft and the ball screw. Therefore, the number of assembly steps and the number of inspection / test steps can be reduced, so that the cost of the electric power steering device can be reduced. In addition, since there is no work of disassembling and reassembling the motor once, it is easy to maintain the assembly accuracy of the motor.

According to the second aspect, the electric motor shaft and the nut can be connected to each other so as to be able to transmit the torque only by fitting each other in the longitudinal direction of the rack shaft. Therefore, the man-hour for assembling the motor shaft and the nut can be further reduced.

According to a third aspect of the present invention, the motor includes a commutator mounted on the motor shaft and a brush contacting the brush contact surface of the commutator, and the brush contact surface is a surface orthogonal to the motor shaft. The brush can be applied to the brush contact surface of the child from the axial direction of the motor shaft. For this reason, when assembling the motor, the assembling direction of the commutator and the brush can be matched with the assembling direction of the motor shaft. Therefore, assemblability can be improved.

According to a fourth aspect of the present invention, a rack guide for extruding the rear surface is disposed on the rear surface side of the surface of the rack shaft on which the rack is formed, and the rack shaft is located at a position closer to the other end than the threaded portion. Since the bush that supports the rack shaft when it is bent by a predetermined value is arranged, an external force due to a road surface reaction acts or generates a moment at both ends of the rack shaft, and the other end of the rack shaft is bent by a predetermined value. Sometimes can be supported by bushes. Therefore, the other end of the rack shaft does not bend more than the predetermined value. Since the amount of deflection is small, vibration of the rack shaft can be easily suppressed. When the vibration of the rack shaft is suppressed, the vibration of the steering handle is also suppressed, so that the steering feeling is enhanced. Also, vibration transmitted to the vehicle interior via the steering wheel is suppressed,
Noise in the cabin can be prevented. In addition, when the external force or moment is small, the rack shaft does not hit the bush because the amount of deflection is small. Therefore, good steering feeling can be maintained.

[Brief description of the drawings]

FIG. 1 is a schematic view of an electric power steering device according to the present invention.

FIG. 2 is an overall configuration diagram of an electric power steering device according to the present invention.

FIG. 3 is a sectional view taken along line 3-3 in FIG. 2;

FIG. 4 is a sectional view of a main part around a rack shaft, an electric motor, and a ball screw according to the present invention.

FIG. 5 is a cross-sectional view showing a connection structure between a motor and a ball screw according to the present invention.

FIG. 6 is an exploded view showing a connection structure of a motor, a ball screw, and a torque limiter according to the present invention.

FIG. 7 is an explanatory view of an assembling procedure of a motor according to the present invention.

FIG. 8 is a completed view of the electric motor according to the present invention and an explanatory view of an assembling procedure of the electric power steering device.

FIG. 9 is a diagram illustrating the operation of the electric power steering device according to the present invention.

FIG. 10 is an explanatory diagram of a manufacturing procedure of a rack shaft according to the present invention.

FIG. 11 is a schematic diagram of a conventional electric power steering device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Electric power steering apparatus, 21 ... Steering wheel, 24 ... Pinion shaft, 25 ... Rack and pinion mechanism, 26 ... Rack shaft, 29 ... Steering wheel, 31 ...
Steering pinion, 32: rack, 41: steering torque sensor, 50: electric motor, 56: electric motor shaft, 59: commutator, 5
9a: brush contact surface, 61: brush, 70: ball screw, 71: screw portion, 72: ball, 73: nut, 90
... torque limiter, 105 ... bush, 120 ... rack guide.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuo Sugino 1-4-1 Chuo, Wako-shi, Saitama Pref. Inside Honda R & D Co., Ltd. (72) Inventor Yasuhiro Tsutsui 1-4-1 Chuo, Wako-shi, Saitama F-term in Honda R & D Co., Ltd. (reference) 3D033 CA02 CA04 CA16 CA28

Claims (4)

[Claims] 1. A rack is formed on one side of one end of a rack shaft extending in the vehicle width direction, a steering pinion is engaged with the rack, and a screw portion is formed on a portion of the rack shaft other than the rack. By attaching a nut of a ball screw to this screw portion via a ball and connecting a hollow electric motor shaft surrounding the rack shaft to the nut, an auxiliary torque generated by the electric motor according to the steering torque is transmitted from the electric motor shaft. An electric power steering device, wherein the nut is arranged between the rack and the electric motor, the electric power steering device being added to a rack shaft via the nut. 2. The electric power steering apparatus according to claim 1, wherein the motor shaft and the nut are connected to each other in a longitudinal direction of the rack shaft so as to transmit torque. 3. The motor according to claim 1, further comprising: a commutator mounted on the motor shaft, and a brush contacting a brush contact surface of the commutator, wherein the brush contact surface is a surface orthogonal to the motor shaft. The electric power steering device according to claim 1 or 2, wherein 4. A rack guide for extruding the rear surface of the rack shaft on the rear side of the surface on which the rack is formed,
3. A bush that supports the rack shaft when it is bent by a predetermined value at a position closer to the other end than the screw portion of the rack shaft.
Or the electric power steering device according to claim 3.